In operation of mobile telephone networks, signals sent between mobile telephones and base transmission stations (BTSs) include various operating parameters that relates to operation of the mobile telephones, the BTSs, and communication between them.
It is known to determine from measured operating parameters the likely location of a mobile phone and to store data mapping operating parameters to an estimate of location in a database. The database can subsequently be used (for example by a user, network operator or government or other agency) to determine the location of a user's mobile telephone by matching operating data obtained from the user's telephone with operating data stored in the database and determining the location of the mobile telephone from location data associated with the stored operating data. An example of such techniques is described in WO 2007/057594, the content of which is hereby incorporated by reference.
In one example, operating data sent between a BTS and a mobile phone includes timing advance zone (TA zone) information that identifies in which TA zone the mobile phone is located. Usually TA zones are arranged as concentric rings, or circumferential sections of such rings (also referred to as slices) of increasing distance from the BTS. For example, in some known systems each TA zone has a radial thickness of 550 m. By determining which TA zone a mobile phone is in, or by monitoring transitions from one TA zone to another, the location of the user can be estimated. Alternatively, the relative signal strengths received by a mobile telephone from different BTSs can be used to determine an estimate of the location of the mobile telephone.
However, the building and maintenance of databases of mobile network operating data and associated location data that can be used to estimate locations of mobile users is time consuming and costly. Furthermore, the accuracy of the location determination depends on the accuracy with which the mobile phone operating parameters can be used to estimate location.
Known systems for monitoring the performance of mobile networks can provide information concerning the variation of measured mobile phone operating parameters with direct measurements of location. For example in the TEMs system, data for each geographical area is obtained by an operator who drives a vehicle fitted with a custom system comprising a mobile phone, GPS device and associated laptop computer for logging mobile phone parameters around each road in the area. Such systems are intended primarily to assess mobile network performance, and the use of such systems can be time-consuming and expensive (operator costs can be several hundred pounds per hour or more). Furthermore, measurements must be repeated regularly as network performance and the variation of mobile phone operating parameters with location can vary significantly over time.
In an alternative approach, as described in WO 2007/017691, the content of which is hereby incorporated by reference, a known traffic monitoring system (TMS) is used to provide continuous, accurate locations for vehicles moving on the roads. Many drivers or passengers of such vehicles will carry with them mobile phones that may be (intermittently) active during each journey. As described in WO 2007/017691, mobile phone control parameters observed on the mobile network from the mobile phones carried by the drivers or passengers of the vehicles can be stored within a database, and linked to position data obtained from the traffic monitoring system (for example, a specific RF signal level pattern could be uniquely associated with a specific physical location). This stored information can then be used by comparing the mobile phone control parameters of mobile telephones on a network against the parameters stored in the database.
However, the accuracy of the determination of location of a mobile device using the database is still dependent on the mobile phone parameters chosen and the accuracy with which they can be used to determine location. For example, RF signal level patterns can vary over time and with environmental conditions.
It is an aim of the present invention to provide an improved or at least alternative method or apparatus for determining the location of mobile devices from mobile device operating parameters.